写一个句子去重的java函数，谢谢大侠。

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;

public class Test {

private BufferedReader bufIn;
private BufferedWriter bufOut;
private HashMap<String, String> map = new HashMap<String, String>();

public Test() {
try {
String str = "";
bufIn = new BufferedReader(new FileReader("input.txt"));
while ((str = bufIn.readLine()) != null) {
map.put(str, "a");
}

bufOut = new BufferedWriter(new FileWriter("output.txt", true));
Iterator<String> it = map.keySet().iterator();
while (it.hasNext()) {
Object key = it.next();
bufOut.write(key.toString());
bufOut.newLine();<